DESCRIPTION

For more details about the meaning of arguments see the
PEM FUNCTION ARGUMENTS section.

Each operation has four functions associated with it. For
clarity the term "foobar functions" will be used to collectively
refer to the PEM_read_bio_foobar(), PEM_read_foobar(),
PEM_write_bio_foobar() and PEM_write_foobar() functions.

The PrivateKey functions read or write a private key in
PEM format using an EVP_PKEY structure. The write routines use
``traditional'' private key format and can handle both RSA and DSA
private keys. The read functions can additionally transparently
handle PKCS#8 format encrypted and unencrypted keys too.

PEM_write_bio_PKCS8PrivateKey() and PEM_write_PKCS8PrivateKey()
write a private key in an EVP_PKEY structure in PKCS#8
EncryptedPrivateKeyInfo format using PKCS#5 v2.0 password based encryption
algorithms. The cipher argument specifies the encryption algorithm to
use: unlike all other PEM routines the encryption is applied at the
PKCS#8 level and not in the PEM headers. If cipher is NULL then no
encryption is used and a PKCS#8 PrivateKeyInfo structure is used instead.

PEM_write_bio_PKCS8PrivateKey_nid() and PEM_write_PKCS8PrivateKey_nid()
also write out a private key as a PKCS#8 EncryptedPrivateKeyInfo however
it uses PKCS#5 v1.5 or PKCS#12 encryption algorithms instead. The algorithm
to use is specified in the nid parameter and should be the NID of the
corresponding OBJECT IDENTIFIER (see NOTES section).

The PUBKEY functions process a public key using an EVP_PKEY
structure. The public key is encoded as a SubjectPublicKeyInfo
structure.

The RSAPrivateKey functions process an RSA private key using an
RSA structure. It handles the same formats as the PrivateKey
functions but an error occurs if the private key is not RSA.

The RSAPublicKey functions process an RSA public key using an
RSA structure. The public key is encoded using a PKCS#1 RSAPublicKey
structure.

The RSA_PUBKEY functions also process an RSA public key using
an RSA structure. However the public key is encoded using a
SubjectPublicKeyInfo structure and an error occurs if the public
key is not RSA.

The DSAPrivateKey functions process a DSA private key using a
DSA structure. It handles the same formats as the PrivateKey
functions but an error occurs if the private key is not DSA.

The DSA_PUBKEY functions process a DSA public key using
a DSA structure. The public key is encoded using a
SubjectPublicKeyInfo structure and an error occurs if the public
key is not DSA.

The DSAparams functions process DSA parameters using a DSA
structure. The parameters are encoded using a Dss-Parms structure
as defined in RFC2459.

The DHparams functions process DH parameters using a DH
structure. The parameters are encoded using a PKCS#3 DHparameter
structure.

The X509 functions process an X509 certificate using an X509
structure. They will also process a trusted X509 certificate but
any trust settings are discarded.

The X509_AUX functions process a trusted X509 certificate using
an X509 structure.

The X509_REQ and X509_REQ_NEW functions process a PKCS#10
certificate request using an X509_REQ structure. The X509_REQ
write functions use CERTIFICATE REQUEST in the header whereas
the X509_REQ_NEW functions use NEW CERTIFICATE REQUEST
(as required by some CAs). The X509_REQ read functions will
handle either form so there are no X509_REQ_NEW read functions.

The X509_CRL functions process an X509 CRL using an X509_CRL
structure.

The PKCS7 functions process a PKCS#7 ContentInfo using a PKCS7
structure.

The NETSCAPE_CERT_SEQUENCE functions process a Netscape Certificate
Sequence using a NETSCAPE_CERT_SEQUENCE structure.

PEM FUNCTION ARGUMENTS

The PEM functions have many common arguments.

The bpBIO parameter (if present) specifies the BIO to read from
or write to.

The fpFILE parameter (if present) specifies the FILE pointer to
read from or write to.

The PEM read functions all take an argument TYPE **x and return
a TYPE * pointer. Where TYPE is whatever structure the function
uses. If x is NULL then the parameter is ignored. If x is not
NULL but *x is NULL then the structure returned will be written
to *x. If neither x nor *x is NULL then an attempt is made
to reuse the structure at *x (but see BUGS and EXAMPLES sections).
Irrespective of the value of x a pointer to the structure is always
returned (or NULL if an error occurred).

The PEM functions which write private keys take an enc parameter
which specifies the encryption algorithm to use, encryption is done
at the PEM level. If this parameter is set to NULL then the private
key is written in unencrypted form.

The cb argument is the callback to use when querying for the pass
phrase used for encrypted PEM structures (normally only private keys).

For the PEM write routines if the kstr parameter is not NULL then
klen bytes at kstr are used as the passphrase and cb is
ignored.

If the cb parameters is set to NULL and the u parameter is not
NULL then the u parameter is interpreted as a null terminated string
to use as the passphrase. If both cb and u are NULL then the
default callback routine is used which will typically prompt for the
passphrase on the current terminal with echoing turned off.

The default passphrase callback is sometimes inappropriate (for example
in a GUI application) so an alternative can be supplied. The callback
routine has the following form:

int cb(char *buf, int size, int rwflag, void *u);

buf is the buffer to write the passphrase to. size is the maximum
length of the passphrase (i.e. the size of buf). rwflag is a flag
which is set to 0 when reading and 1 when writing. A typical routine
will ask the user to verify the passphrase (for example by prompting
for it twice) if rwflag is 1. The u parameter has the same
value as the u parameter passed to the PEM routine. It allows
arbitrary data to be passed to the callback by the application
(for example a window handle in a GUI application). The callback
must return the number of characters in the passphrase or 0 if
an error occurred.

EXAMPLES

Although the PEM routines take several arguments in almost all applications
most of them are set to 0 or NULL.

NOTES

The old PrivateKey write routines are retained for compatibility.
New applications should write private keys using the
PEM_write_bio_PKCS8PrivateKey() or PEM_write_PKCS8PrivateKey() routines
because they are more secure (they use an iteration count of 2048 whereas
the traditional routines use a count of 1) unless compatibility with older
versions of OpenSSL is important.

The PrivateKey read routines can be used in all applications because
they handle all formats transparently.

A frequent cause of problems is attempting to use the PEM routines like
this:

X509 *x;
PEM_read_bio_X509(bp, &x, 0, NULL);

this is a bug because an attempt will be made to reuse the data at x
which is an uninitialised pointer.

PEM ENCRYPTION FORMAT

This old PrivateKey routines use a non standard technique for encryption.

The line beginning DEK-Info contains two comma separated pieces of information:
the encryption algorithm name as used by EVP_get_cipherbyname() and an 8
byte salt encoded as a set of hexadecimal digits.

After this is the base64 encoded encrypted data.

The encryption key is determined using EVP_BytesToKey(), using salt and an
iteration count of 1. The IV used is the value of salt and *not* the IV
returned by EVP_BytesToKey().

BUGS

The PEM read routines in some versions of OpenSSL will not correctly reuse
an existing structure. Therefore the following:

PEM_read_bio_X509(bp, &x, 0, NULL);

where x already contains a valid certificate, may not work, whereas:

X509_free(x);
x = PEM_read_bio_X509(bp, NULL, 0, NULL);

is guaranteed to work.

RETURN CODES

The read routines return either a pointer to the structure read or NULL
if an error occurred.